This invention concerns noise control devices for a room that increases the decay rate of room resonances without excessively dampening the acoustical brightness of the room.
U.S. Pat. No. 4,362,222 to Hellstrom discloses a dampener unit for corner placement. The benefits from noise control methods so placed are outlined in the patent noting particularly low frequency absorbtion without the use of Helmholtz resonators. An absorbive panel extends diagonally across a room intersection of a ceiling and wall and establishes a volume with a flow resistive surface that faces pressure fluctuations resulting from reflecting sound waves.
Diffraction type sound absorbers are found in many variations. Some are filled with fiberglass while others have a hollow interior with a fiberglass blanket skin. Some sound dampeners incorporate Helmholtz resonators to enhance low frequency absorption with maximum sound absorption their common goal. U.S. Pat. No. 2,160,638 by Bedell discloses a fiber packed tube with a perforate metal skin. U.S. Pat. No. 2,502,020 shows a perforate metal skin with a hollow interior and a fiber liner immediately inside the skin. U.S. Pat. No. 2,706,530 shows a rectangular suspended absorbant with openings to introduce the resonator aspect. U.S. Pat. No. 4,319,661 shows a unit which places discrete Helmholtz resonators at the ends of the Bedell type tube, for low frequency absorbtion of around 125 Hz.
The extensive use presently of acoustical tiles in ceilings and upper wall surfaces serves to control the decay rates of higher frequencies above 500 Hz. In order to absorb energy in the low frequency range, a large amount of absorbant material is often used and undesirably the acoustical brightness of a room is thereby diminished. The modern room, with its higher frequency decay rate controlled by standard architectural acoustical wall and ceiling treatments still however has a major problem in the control of room resonance and lower frequency decay rates.
Important objects of the present invention include the provision of an acoustical device which serves to dampen low frequency sound waves while reflecting higher frequencies so as to enhance room acoustics; the provision of an acoustical device which is adapted for placement in a room tri-corner for optimum performance; the provision of a sound dampener of a free standing type having nonuniform dampening and reflective qualities.